CHEMISTRY COMMUNITY

Which atom in a molecule is drawn lower than the other in a MO diagram? How much lower do you draw it?

The atom that is more electronegative is drawn lower in the MO diagrams. I think that there is no exact way to measure how much lower to draw it (that we are able to do right now), so just make sure that it is obvious that the energy level is lower.

If you look up the molecular orbital diagram for NO-, you can see just about how much lower the more electronegative atom is drawn (in this case, oxygen)

I believe the amount of distance you draw between them is due to the difference is electronegativity. So if one of the atoms is much less electronegative, it will be much higher than the one that is much more electronegative. On the other hand, if the difference in electronegativity between the two atoms is not great, they will be drawn closer together but the less electronegative one will still be slightly higher, and the more electronegative one will be slightly lower.

Rachel's response is correct. The reason why the orbitals for N and O going are uneven with each other is because O is more electronegative than N. Because of is more electronegative than N, the orbitals require more energy to fill or remove electrons from, which is why they are located higher than the N orbitals, because they have higher energy levels. As long as you differentiate between "hetero" MO diagrams and visibly draw the orbitals of the more electronegative orbital higher, you should be fine.